1. Field of the Invention
The present invention relates in general to medical valve devices, in particular, to an artificial valve that is readily percutaneously inserted into a vein, as well as implanted into a prosthetic graft to be used for a bypass in the venous system. Further, the present invention relates in general to catheter devices, in particular, to a catheter device capable of measuring an internal diameter of a body cavity such as an artery or vein, as well as for measuring the internal diameter of other tubular structures such as a bile duct, bronchus or ureter.
2. Description of Prior Developments
Progress in surgery for venous disease has lagged far behind developments in other areas such as arterial surgery. The propulsive force of the left ventricle of the heart makes the arterial tree a high pressure and high velocity system. In contrast, the venous system is characterized by low pressure and low velocity. Effective venous return is dependent on the functioning of venous valves, patency of veins and the contraction of the peripheral muscles, known as the "venous pump".
Valvular incompetence occurs when the natural venous valves do not function properly. This can be either congenital or acquired. When valves become incompetent, the direction of blood flow in a vein is reversed due to the effect of gravity, increased pressure within the abdominal cavity, or other conditions causing venous compression. Acquired incompetence is usually a consequence of venous thrombosis, which is when a blood clot forms in a vein. Thrombosis is followed by formation of fibrous tissue, which destroys the normal structure and function of the valves, causing valvular incompetence and venous insufficiency.
Loss of venous patency, i.e., venous thrombosis or obstruction, results from conditions such as stasis, reduced blood volume, injury to the inner lining of the vein, extrinsic compression and thrombotic disorders. Although, an obstruction theoretically can be corrected by a bypass, venous bypasses are rarely performed and are often unsuccessful.
Valvular incompetence and venous obstruction, alone or in combination, lead to chronic venous insufficiency. This often causes permanent disability due to pain, swelling, and ulceration of the lower limbs, and places the patient at high risk for recurrent thrombosis and pulmonary embolism. Treatment is difficult, prolonged, and often unsuccessful. These patients require home care, frequent office visits, and intermittent hospitalization. Consequently, millions of dollars are spent each year for the care of these patients.
Valvular incompetence previously has been treated by a number of procedures including the direct repair of incompetent valves, vein transfer, vein segment transfer, or venous bypass using a competent valve. A vein transfer involves the surgical transfer of a vein with incompetent valves to one with normally functioning valves. A vein segment transfer involves transferring a vein segment with a normal valve to other veins with defective valves. However, these procedures are rarely performed since such procedures are usually only applicable to a limited number of patients. Moreover, these operations are technically difficult to perform and the results are poor.
Chronic venous obstruction has previously also been treated by other procedures including an autogenous vein bypass and a prosthetic graft bypass. However, these procedures have also been found to be less than satisfactory since both can only be used in a few select cases with limited success.
In particular, the autogenous vein bypass often fails since it provides too small a caliber for bypassing large veins and insufficient length to bypass the obstructed segment. The prosthetic graft bypass is rarely used since it has a high incidence of thrombosis or clotting. Further, all prosthetic grafts are inherently incompetent since there are no valves in the grafts.
Another possible alternative for treating valvular incompetence would be to replace the defective natural valve with an artificial valve. The use of artificial valves is well known in other areas of the vascular system such as the heart. However, these valves are not adaptable to veins due to a number of unique requirements. For example, a venous valve would have to be designed to operate in a low pressure and low flow system. Further, a venous valve would have to be smaller in diameter and reinforced to prevent being compressed by outside forces.
Although, artificial venous valves have not been used in patients so far, the prior art does include a number of such devices. For example, U.S. Pat. No. 4,851,001 to Taheri, issued Jul. 25, 1989, and U.S. Pat. No. 5,607,465 to Camilli, issued Mar. 4, 1997, both disclose an artificial valve for use in blood vessels. However, the valve devices disclosed in these patents have a number of problems. For example, such devices are not generally readily percutaneously inserted into a blood vessel. Further, such devices generally make no provision for measuring the internal diameter of the vein at the proposed site of placement.
However, the prior art does disclose the devices for measuring internal diameters. For example, U.S. Pat. No. 3,661,148 to Kolin, issued May 9, 1972, and U.S. Pat. No. 5,010,892 to Colvin et al., issued Apr. 30, 1998, discloses such devices.
However, in regard to veins such devices have problems. For example, such devices do not directly measure the internal diameters. Such devices are also not specifically intended for use in blood vessels. Further, such devices are not versatile enough to perform other functions.